Field of the Invention
The present invention relates to a method and a device for automatic checking designed to detect, to measure, to watch possible cracks and other damage in mechano-weld assemblies, non-destructively.
The invention relates more particularly to a vehicle moving inside a hollow body, bearing a robot arm serving to position measuring probes in contact with areas to be checked.
Whether it relates to complying with the requirements of quality in manufacture (initial control) or monitoring changes during use (possible damage, corrosion, fatigue . . . ), it is in a good many cases necessary and required by regulations to ensure the soundness of a structure and to give warning of the risk of accident. These diagnoses have already been imposed on nuclear power stations, for example, and they will soon be likewise required more critically on off-shore platforms.
At present and even for the aforementioned example, in a good many cases testing is carried out manually, which considerably limits the confidence which can be expected of these measurements (off-shore) or requires an appreciable time and involves the absorption of radiation for the operators (nuclear power stations).
In its nature, the method used here measures the parameters defining a defect: location, orientation, dimensions. It is compatible with memorization of all the corresponding values; in addition, being automatic it overcomes uncertainties which accompany any manual method.
It is particularly intended for the inspection of tubular assembly welds where one of the elements is accessible from the inside. It responds to difficult environmental conditions, whether it relates to a confined space or a hostile environment such as that in nuclear power stations or off-shore. It is suitable for checking tubular assemblies whether it relates to the joining up of pipes, cappings, or again tubular trellis works with their fastening nodes between the principal members (barrels or piers, cords) and secondary members (bracings).
In the case, for example, of off-shore platforms, which attain huge sizes, welds are counted in hundreds. The trellis-work nodes include up to 6 to 8 bracings with or without stiffening gussets. These welds coincide with particularly stressed zones liable through their complex nature to be subjected to manufacturing defects, and through their situation subject to alternating stresses which can generate fatigue cracks.
It is an object of the invention to provide a method enabling direct, exhaustive, precise and rapid reproducible measurements of such welded joints and which do not require the intervention on site of an operator.
It is another object of the invention to provide a method which responds to the exigencies of surveillance in service ("in-service inspection").
It is another object of the invention to provide a device for performing the last-mentioned methods by positioning positively and orienting correctly the measuring sensors within some millimeters with respect to the weld beads and to explore under these conditions the integrity of the weld bead (scanning of the weld by sensors).